Squid skin is covered in far more hair-like sensory cells than scientists realized, and the animals may tune those cells to different water movements in a way that resembles the human inner ear. Researchers at Case Western Reserve University and the Marine Biological Laboratory in Woods Hole, Massachusetts, reported the findings in Current Biology.

Scientists already knew squid had hair cells on their heads and arms. Using a 3D imaging technique, the new work found hundreds more spread across the entire body, the first full-body map of the squid's lateral line, a sensory system that detects water movement.

The study matters for two reasons. For medicine, squid offer a new model for studying the hair bundles whose damage underlies most human deafness. For the ocean, it shows how heavily these commercially important animals rely on sensing water vibrations, at a time when human-made underwater noise is rising.

Mapping Every Hair Cell on a Hatchling

The team studied hatchlings of the longfin inshore squid, Doryteuthis pealeii, a species found along the U.S. Atlantic coast, according to ScienceAlert. They used light sheet microscopy, which sweeps a thin sheet of laser light through a specimen one plane at a time to build a detailed 3D image while limiting damage to tissue.

The researchers described two kinds of arrangements. Some hair cells sit in the linear rows already reported in squid, while others form broad regional patches the team calls lateral line fields. Those fields had not been explicitly described before in squid or fish, according to the study.

"Squid are cephalopods with a diverse population of hair cells on the surface of their bodies," said Brian McDermott, an associate professor at the Case Western Reserve School of Medicine who led the team, in a university release. Carsten Wolff, associate director of imaging at the Marine Biological Laboratory, worked with the Case Western group.

Hair Bundles of Different Lengths

The key finding involves the hair bundles, tiny projections on each cell that bend when water moves. In the squid, bundle length varies by location. Bundles on the mantle, the squid's main body, are much shorter than those on the head.

That variation suggests the squid tunes different groups of cells to different frequencies of water movement — similar to the human cochlea, where taller bundles respond to low pitches and shorter bundles to high pitches. The researchers say squid "seem to" regulate bundle length this way, a cautious framing. Fish lateral lines, by contrast, have bundles of uniform length, according to the university.

"Anatomical positions and corresponding variation in hair bundle lengths suggest some lateral lines detect distinct stimuli," the team wrote in the paper.

A Window Into Human Hearing Loss

The medical interest comes from how hair cells fail. "Often, when a child is born deaf or a hearing person loses their hearing, it is the hair bundle that has been damaged," McDermott said, adding that studying the squid's hair bundle "holds promise for understanding how hearing loss occurs."

Human hair cells are hard to study because they sit deep inside the skull, encased in bone. Animals with hair cells on the outside of their bodies offer easier access. McDermott's lab previously used the same logic with zebrafish, showing in a 2023 study that their skin hair cells are tuned to sense different water directions.

Several limits apply — and the researchers acknowledge them. The study examined only hatchlings of one species, and the tuning idea is an inference from anatomy rather than a direct measurement of what each cell detects. The research does not test any hearing-loss treatment, and its medical value remains a possibility for future work.

Squid Senses in a Noisier Ocean

Squid are already a classic laboratory animal. Their giant nerve fibers helped scientists in the mid-20th century work out how nerve signals travel, research that earned a Nobel Prize, and the Marine Biological Laboratory has long supplied longfin squid for that kind of work. Adding a full-body map of their hair cells extends that legacy into hearing research.

The findings also highlight how much squid rely on detecting vibrations in water to find prey, avoid predators and navigate. Longfin inshore squid support a commercial fishery off the U.S. East Coast and are an important food source for fish, seabirds and marine mammals.

Underwater noise from shipping, construction and seismic surveys has grown in recent decades. Earlier research, including a 2011 study led by bioacoustician Michel André, found that intense low-frequency sound damaged sensory hair cells in the balance organs of squid and other cephalopods. The new study did not test noise effects, but a fuller map of where squid hair cells sit could help scientists study which parts of the body are most exposed.

The longfin squid's role in the food web also makes its senses relevant to fisheries science. How well squid detect predators and prey can influence their survival, and in turn the fish, seabirds and marine mammals that depend on them.

Researchers next hope to test how squid hair cells respond to specific water movements and whether the bundle-length pattern holds in adults. An ongoing three-year Marine Biological Laboratory fellowship program studying how squid hear is one avenue for that work.

The bottom line is that squid carry a far more extensive set of water-sensing hair cells than scientists knew, possibly tuned like a human ear. The finding opens a new route for hearing research and a sharper picture of how a key ocean species senses its world.

What Readers Want to Know

What did researchers discover about squid?

They found hundreds of previously unknown hair cells across the squid's body and produced the first full-body map of its lateral line, a system that senses water movement.

How are squid hair cells like human ears?

Their hair bundles vary in length by body location, suggesting different cells are tuned to different frequencies, similar to the human cochlea.

Can squid hear?

The hair cells in this study detect water movement rather than sound in the usual sense. Squid also have separate balance organs that can sense low-frequency vibration.

Which squid was studied?

Hatchlings of the longfin inshore squid, Doryteuthis pealeii, a species found along the U.S. Atlantic coast.

Could this help treat hearing loss?

Possibly in the long term. Researchers say squid could be a useful model for studying damaged hair bundles, but the study did not test any treatment.

Does ocean noise affect squid?

Earlier research found intense low-frequency noise can damage cephalopod sensory cells. This study did not test noise effects.